Frederick W. Werner

The triangular fibrocartilage complex of the wrist—Anatomy and function

The anatomy and function of the triangular fibrocartilage complex (TFCC) of the wrist was studied through anatomic dissections and biomechanical testing of 61 specimens. The TFCC was found to be a homogenous structure composed of, but not dissectable into, the articular disc, the dorsal and volar radioulnar ligaments, the meniscus homologue, the ulnar collateral ligament, and the sheath of the extensor carpi ulnaris. The TFCC was found to be perforated in 53% of specimens dissected, and all of the wrists with a demonstrable perforation showed evidence of damage or erosion of the cartilage of the lunate and/or distal ulna. Biomechanical studies suggest that the TFCC functions both as a cushion for the ulnar carpus and as a major stabilizer of the distal radioulnar joint. Perforations of the TFCC can result in the ulna-lunate abutment and cartilage erosion. Since excision of the TFCC may lead to ulnolunate abutment, chronic wrist pain, and/or instability of the distal radioulnar joint, it is not recommended.

Biomechanics of the distal radioulnar joint.

The distal radioulnar joint is an intricate part of wrist function. The radius and hand move in relation to, and function about, the distal ulna. Significant loads are transmitted to the forearm unit through the distal ulna via the triangular fibrocartilage. The anatomic relations between the distal radius and ulna and the ulnar carpus are precise, and even minor modifications in these relations leads to significant load-pattern changes. The authors can only speculate on the clinical ramifications of such load-pattern modifications. Since M. DeSaults dissertation on dislocation of the distal radius, published in 1791, much has been written on injuries to, and afflictions of, the radiocarpal area. Although injuries and afflictions in this area undoubtedly have not changed throughout the years, an increasing variety of ulnar wrist syndromes and treatment programs are being recognized. This phenomenon attests not only to the need for continuous investigations of wrist problems but also to the great excitement that presently exists in the field. Better understanding of the anatomy and newer knowledge of the biomechanics of the distal radioulnar joint should herald an ulnar wrist renaissance.

Functional wrist motion: a biomechanical study

A triaxial electrogoniometer was used to measure functional wrist motion. Wrist motion was evaluated in 10 normal subjects who performed 52 standardized tasks. The wrist joint was found to have three degrees of freedom (flexion-extension, radioulnar deviation, and rotation). The normal functional range of wrist motion is 5 degrees of flexion, 30 degrees of extension, 10 degrees of radial deviation, and 15 degrees of ulnar deviation.

Ulnar variance determination

A template utilizing curves of various radii has been developed for accurately measuring ulnar variance from standard posterioranterior radiographs of the wrist. It has been determined that this measurement can most accurately and consistently be performed with the forearm in neutral (0°) rotation and the elbow flexed 900°.

A biomechanical study of distal radial fractures

In an attempt to explain disability in dorsally angulated malunited distal radius fractures, an experiment was designed to evaluate load patterns about the wrist with varying degrees of dorsal angulation of the distal radius. Osteotomies were made in the distal radius of fresh cadaver arms after a modified external fixator was applied to the radius and load cells applied to the proximal radius and ulna. Pressure-sensitive film was inserted into the radioulnar carpal joint. After a predetermined load was applied to the wrist it was found that the load through the ulna increased from 21% to 67% of the total load as the angulation of the distal radial fragment increased from 10 degrees of palmar tilt to 45 degrees of dorsal tilt. The pressure distribution on the ulnar and radial articular surfaces changed in position and became more concentrated as dorsal angulation increased.

The stabilizing mechanism of the distal radioulnar joint during pronation and supination

A biomechanical cadaver study was performed to determine the roles of the stabilizing structures of the distal radioulnar joint during pronation and supination. Subluxation and dislocation of the radius with respect to the ulna were evaluated in seven cadaver forearms placed in supination, pronation, and neutral forearm rotation. The amount of subluxation was measured with all structures intact, and after sectioning in various sequences the dorsal and palmar radioulnar ligaments, the distal portion of the interosseous membrane including the pronator quadratus, and the entire interosseous membrane. After sectioning two of any four structures, the distal radioulnar joint remained stable. When the interosseous membrane was disrupted first, the dorsal radioulnar ligament was found to be more important than the palmar radioulnar ligament in stabilizing the distal radioulnar joint in pronation, and conversely the palmar radioulnar ligament was more important than the dorsal radioulnar ligament in supination. Dislocation, and frequently diastasis, occurred only with sectioning of all four structures. This suggests that all four structures contribute to stability of the distal radioulnar joint.

Relationship between ulnar variance and triangular fibrocartilage complex thickness

The thickness of the thinnest aspect of the articular disc portion of the triangular fibrocartilage complex (TFCC) was experimentally measured and compared with ulnar variance. There is an inverse relationship between positive ulnar variance and TFCC thickness.

The effect of dorsally angulated distal radius fractures on distal radioulnar joint congruency and forearm rotation

A biomechanical cadaver study was performed to evaluate the effect of dorsally angulated distal radius fractures on the distal radioulnar joint. Frykman I distal radius fractures were simulated, and laxity measurements were taken with and without sectioning the triangular fibrocartilage complex and the interosseous membrane. The findings of this study were threefold. First, measured in terms of radial diastasis, incongruency of the distal radioulnar joint occurred with increasing dorsal tilt of the distal radius. It became most dramatic with a change of more than 20 degrees of dorsal angulation of the distal radius. This corresponds to approximately 10 degrees of dorsal tilt of the articular surface of the distal radius, as measured on an x-ray film. Second, increased dorsal angulation caused interosseous membrane tightness and limited maximum pronation and maximum supination. Third, distal radioulnar joint dislocation did not occur until both the triangular fibrocartilage complex and interosseous membrane were sectioned. These results reveal the importance of anatomic reduction of the distal radius fracture and evaluation of damaged soft tissue structures.

Tensile strength of the cement-bone interface depends on the amount of bone interdigitated with PMMA cement

An experimental investigation was performed to (1) determine the general mechanical behavior and in particular, the post-yield behavior of the cement-bone interface under tensile loading, (2) determine where interface failure occurs, and (3) determine if the mechanical properties of the interface could be related to the density of bone at the interface and/or the amount of cement-bone interdigitation. Seventy-one cement-bone test specimens were machined from human proximal femurs that had been broached and cemented using contemporary cementing techniques. The amount of cement-bone interdigitation was documented and the quantitative computed tomography equivalent mineral density (QCT density) of the bone with cement was measured. Specimens were loaded to failure in tension under displacement control and exhibited linear elastic behavior with some reduction in stiffness until the peak tensile stress was reached (1.28 +/- 0.79 MPa). A substantial amount of strain softening (negative tangent stiffness) with an exponential-type decay was found after the peak stress and continued until there was complete debonding of the specimens (at 0.93 +/- 0.44 mm displacement). Interfacial failure most often occurred at the extent of cement penetration into the bone (56% of specimens) or with small spicules of cement left in the bone (38% of specimens). The results showed that the post-yield tensile behavior contributes substantially to the energy required to cause failure of the cement-bone interface, but the post-yield behavior was not well correlated with the amount of interdigitation or density of bone. Linear regression analysis revealed a moderate (r2 = 0.499, p < 0.0001) positive relationship between the tensile strength of the cement-bone interface and the quantity of bone interdigitated with the cement.

The interosseous membrane of the forearm: Anatomy and function

The anatomic detail of the interosseous membrane was studied by dissection of 20 preserved cadaveric specimens. The interosseous membrane was found to be a complex structure consisting of a central band, accessory bands, a proximal interosseous band, and membranous portions. The central band, a stout ligamentous structure, was found in all specimens. Fibers of the central band originate on the radius and are oriented distal and ulnar an average of 21 degrees to the longitudinal axis of the ulna. Accessory bands were of less substance than the central band but were present in all specimens. The number of accessory bands ranged from 1 to 5. The proximal interosseous band is located on the dorsal surface only, and its fibers run counter to the central band. It shares a point of origin with the central band on the radius. This structure was present in 17 of 20 specimens. Since the central band was the most dominant and consistent structure, we chose to analyze the strain in the central band in 6 preserved specimens. Maximum strain in the central band of the intact specimen occurs in neutral forearm rotation. Once the radial head is removed, the percent strain universally increases throughout the arc of forearm rotation and peak strain shifts to pronation.